1. Field of the Invention
The present invention relates to a sound signal processing apparatus and a sound signal processing method and, more particularly, to a sound signal processing apparatus and sound signal processing method which generate a sound signal output to a phase inversion type speaker.
2. Description of the Related Art
As a technique for improving the bass reproduction characteristics of a speaker, a phase inversion type speaker is known, which comprises a resonance output unit such as bass-reflect ports or a passive radiator.
A sound output from a general phase inversion type speaker will be described below with reference to FIGS. 7 and 8. FIG. 7 is a connection diagram of a phase inversion type speaker 7 and an amplifier 6 which drives it. The phase inversion type speaker 7 shown in FIG. 7 includes a speaker unit 7a and a resonance output unit 7b. The phase inversion type speaker 7 spatially synthesizes an input voltage from a sound signal input unit 1 with output sound pressures from these units to obtain, as a result, a total output sound pressure.
FIG. 8 shows the schematic waveforms of an input voltage to the sound signal input unit 1, output sound pressures from the speaker unit 7a and resonance output unit 7b of the phase inversion type speaker 7, and total output pressure obtained by spatially synthesizing them. The phase inversion type speaker 7 increases the sound pressure of the low range by using the phenomenon that resonance is made to occur at a frequency with an emission delay time 30 corresponding to an almost half period by accumulating sound pressure emitted from the back surface of the speaker unit 7a in the box internal volume and making the resonance output unit 7b emit the sound pressure with a delay.
In the phase inversion type speaker 7, sound emitted from the back surface of the speaker unit 7a through the resonance output unit 7b with a delay interferes with sound emitted from the front surface of the speaker unit 7a. In order to solve this inconvenience, there has been proposed a speaker system which prevents interference with sound emitted from an acoustic tube mounted on the back surface of the speaker by inverting the phase of the sound using bass-reflect ports provided on the front surface of the speaker unit 7a (see, for example, Japanese Patent Laid-Open No. 63-120586).
In the phase inversion type speaker 7 described above, however, the emission delay time 30 occurs before the resonance output unit 7b emits the sound pressure emitted from the back surface of the speaker unit 7a in the bass range.
In addition, even after the speaker unit 7a stops vibrating, delayed bass sound is emitted due to the spring action generated by the air in the box internal volume and the equivalent weight action generated by the resonance output unit 7b such as a bass-reflect port shape or a passive radiator weight. That is, as shown in FIG. 8, the resonance output unit 7b emits the bass sound delayed by a convergence time 31. Therefore, in addition to the problem that sound in the bass range is emitted with a delay with respect to sound in the treble range, if a high frequency signal exists immediately after the stop of vibration, the sound pressure emission times overlap and may cause disturbances such as masking.